Many products, such as electronic devices, medical devices and pharmaceuticals, are sensitive to water vapor and ambient gases, and exposure to them causes product deterioration and/or product performance degradation. Consequently, blocking coatings or materials are commonly used as a protective measure to safeguard against such undesired exposure.
Plastic coating or films are frequently used as blocking materials. Unfortunately, they suffer from poor gas and liquid permeation resistance, which have values that are typically several orders of magnitude below the requisite value of permeation resistance for acceptable product performance. By way of example, certain LED display and solar cell encapsulation applications require water vapor transmission on the order of <10−4 grams/square meter/day, and in contrast, the water vapor transmission rate for Polyethylene Terephthalate (PET), a commonly used plastic film, is in the order of between about 1 and about 10 grams/square meter/day. Those skilled in the art will recognize that water vapor transmission can be thought of as being inversely proportional to water permeation resistance.
Other approaches protect against exposure to undesired elements by applying a blocking coating to plastic films like PET, to reduce water vapor permeability. These coatings are typically single layers of inorganic materials like Al, SiOx, AlOx and Si3N4, deposited onto the plastic substrates using well-known vacuum deposition processes. A single layer coating of these inorganic materials typically will reduce the water vapor permeability of PET from 1.0 to 0.1 grams/square meter/day. Thus, single blocking coating on a plastic substrate also fails to meet a requisite value of permeation resistance.
Regardless of whether a single plastic film or a plastic substrate with a blocking coating or material is used as a protective measure, conventional diffusion retarding schemes described above fail to protect an underlying device or product to the requisite extent for a particular application (e.g., solar cell application and LED display application). Specifically, the defects present in the inorganic layer are not effectively filled-in and provide a diffusion pathway for moisture and undesired ambient gases to travel from the surface of the blocking layer to the polymer substrate. Consequently, conventional polymeric films are not able to adequately protect the underlying product that it encapsulates from exposure to moisture and undesired ambient gases. As a result, the underlying product degrades over time, eventually failing and suffering from a relatively shorter life span.
What is, therefore, needed are novel barrier layer designs that effectively protect underlying moisture and gas sensitive products from moisture and undesired ambient gases, and that do not suffer from the drawbacks encountered by conventional designs of films alone or with a blocking coating.